In general, cracks in the floor are not a cause for concern. The only time you might worry is if the cracks start to change vertically, suggesting that some settlement is taking place. Tight cracks are common in concrete slabs. In general, if the crack is stable and does not leak water, it does not indicate a structural problem.
In most cases, these are shrinkage cracks that formed when the concrete cured. Most cracks in non-structural concrete slabs are due to failure to follow one or more of the proper procedures. For example, concrete finishers can add too much water to the concrete mix to make it more malleable. They may also need to rehydrate the concrete after prolonged exposure to heat.
When this water evaporates, the concrete fractures and contracts in volume. These cracks are called fine cracks (or shrinkage cracks). After heavy rain or snow melt when the ground below is soft and damp, excessive weight on the slab can press the concrete down and cause cracking. In the pillars, steel posts are inserted into the unstable ground to reinforce it, and hydraulic jacks are used to stabilize the concrete slabs if the subfloor has caused movement.
A concrete slab without reinforcement cracks substantially more than a reinforced slab and is weaker. Some shrinkage cracks are normal, but cracks throughout the slab are a sign that the concrete does not meet standards, may be weaker and less durable than necessary. Since these occurred shortly after the slab was poured, they were most likely due to concrete shrinkage. In most cases, this is due to an uneven seat for the slab itself, such as a poorly compacted subsoil, invasive pressure from tree roots, previous concrete slabs that have not been removed, or repeated expansions and contractions in the rebar.
When concrete expands, it pushes against anything that stands in its way (a brick wall or an adjacent slab, for example). Because many tile cracks are cosmetic, the cost often exceeds the benefit; therefore, it is common and reasonable to see minor cracks in residential concrete slabs. If, on the other hand, the concrete does not meet industry or building code standards, the optimal solution may be to demolish the slab and start an extreme solution again, but better than building on a weak foundation. They do this by placing control joints on concrete slabs, often 10 to 20 feet apart and in both directions.
Slab lift is best suited for leveling smaller slabs of poured concrete because hole placement is more likely to be accurate. When you see a crack in the concrete slab or wall, the first assumption is that something has been done wrong, but that's not always the case. Then, a thin non-structural concrete slab is poured over the rest of the base (a monolithic slab). If a structural contractor drives a piece of heavy equipment loaded with wood onto a 4-inch thick concrete slab, it can crack green (not fully cured) concrete.
Concrete may be thicker at load-bearing points within walls, but other than these points, the rest of the slab is not considered a load-bearing structural element. So, of course, it's frustrating to spot fine cracks, especially if you've just paid for a new driveway, concrete slab, walkway, or garage floor.